Aatrox passive not working

Recently I played a game where I was playing rumble against an aatrox. At one point at level 3 or 4 aatrox had a full passive bar but I hit him with an overheated enhanced auto attack and he died without the passive activating. I do not know if this is a bug with the interaction between overheat and aatrox's passive or if it is just a bug in general but it is potentially game changing and needs to be fixed if possible.